1. Field of the Invention
This invention relates to a power source control system for controlling the power supply to a system having an electronic device such as a personal computer and an expansion unit which is connected to the electronic device to expand the function of the electronic device and which has a power source independent from that of the electronic device.
2. Description of the Related Art
In recent years, portable computers such as lap-top type computers and book type computers have been widely used as small electronic devices which can be easily carried. This type of portable computer is formed with the function of the computer main body suppressed to minimum to enhance the portability thereof. Therefore, an expansion unit is provided separately from the computer main body to permit the computer main body to expand the function by connecting the computer to the expansion unit.
Power sources are independently provided for the computer main body and expansion unit, respectively. Generally, the expansion unit has a function of the A.C. adapter so as to supply a D.C. power to the computer main body. That is, the function expansion unit can be used to supply electric power necessary for charging and operating the computer main body when it is connected to the computer main body.
The expansion unit has a power source switch, and a preset electric power is supplied to the computer main body by turning on the switch to set the power source into the ON state. Since the expansion unit is operated to provide the expanded function of the computer main body whose function is to be expanded when it is connected to the computer main body, the power source switch will not be independently turned on to set the power source into the ON state. However, when the power source switch is turned on to set the power source into the ON state for any reason, it is generally difficult to recognize the ON state of the power source. For this reason, the ON state of the power source may be maintained for a long period of time even if the function expansion unit is not actually used, and in this period of time of the ON state, the power supply to the computer main body connected to the expansion unit is maintained. Thus, in the conventional expansion unit, the possibility that electric power will be uselessly consumed and the elements constructing the unit will be damaged is high. Further, a problem that an error will be caused by a sneak path of the power source at the time of connection or disconnection of the unit occurs.
In a case where the power source of the expansion unit is instantaneously interrupted or set into an abnormal state and an erroneous operation or the power-off occurs while the computer main body is connected to the expansion unit and operated, the computer main body cannot recognize the erroneous operation or power-off. For example, in a case where the expansion unit is set into an abnormal state and the power supply is interrupted when the computer main body is operated by the power supplied from the expansion unit, the computer can effect the normal operation since the computer main body has a battery provided therein and the power is supplied from the battery to the computer main body. Thus, since the computer main body performs the normal operation without recognizing the abnormal state of the expansion unit, the hang-up state may occur.
If the computer main body is set into the hang-up state for the above reason, the user of the computer cannot determine whether the hang-up is caused by the software, computer main body, expansion unit or function expanding elements in the expansion unit. For this reason, the user will use much time and labor to find out the cause of the hang-up. Generally, the cause cannot be found in the above condition and the user will have a deep distrust of the computer or the like.
When only the power source on the expansion unit side is interrupted, a sneak path for the current and voltage will be made from the computer main body side via a signal line including the ground (GND) line. Therefore, when the power source of the expansion unit is turned on again, a latch-up phenomenon occurs in the driver of the expansion unit to damage the parts or cause an erroneous operation.
The computer main body generally has a battery provided therein and can be operated by the battery. In the computer having the battery provided therein, the built-in battery can be removably attached, and in some kinds of computers, different types of built-in batteries having different current capacities can be selectively loaded according to the application.
In some cases, only one kind of computer can be connected to the expansion unit, but recently, an expansion unit to which different kinds of computers can be connected is provided when different kinds of computers are used by using the above type of expansion unit and if optimum currents and voltages required for charging the built-in batteries of the respective computers are equal to each other, it is not necessary to adjust the current and voltage supplied from the expansion unit to the computer. However, when currents and voltages required for charging the built-in batteries of the respective computers are different from each other, it is necessary to adjust the current and voltage supplied from the expansion unit.
For example, when a current and voltage required for charging the built-in battery of a computer connected to the expansion unit are respectively different from the current and voltage supplied from the expansion unit, the battery may be excessively charged or an excessively long time is required for charging the battery.